1. Field of the Invention
The present invention relates to a backup memory control unit preferably serving as a backup to an SDRAM (synchronous DRAM).
2. Description of Related Art
A conventional backup memory control unit using a DRAM (dynamic random access memory) as a backup memory is disclosed in Japanese patent application laid-open No. 11-53271, for example. In this system, a normally energized CPU like a backup microcomputer controls the operating state of the DRAM, and carries out various types of control.
With the foregoing configuration, the conventional backup memory control unit using the DRAM as a backup memory must include the backup microcomputer besides the main CPU. In addition, the runaway risk is growing because of program bugs. Moreover, when the power supply is connected for the first time, it is necessary to turn on the main power supply first to place the DRAM in the self-refresh mode before entering into the backup state. This is because supplying the backup power before placing the DRAM in the self-refresh mode provides a problem of increasing the useless current consumption of the DRAM.